This invention relates to a process for preparing aluminum nitride powder. More particularly, it relates to a process for preparing at a lower temperature and in a shorter period of time, aluminum nitride powder having small particle size and small particle size distribution and also having a uniform shape of particles.
An aluminum nitride sintered body is a material excellent in stability under high temperature and thermal conductivity. Therefore, its use has been developed as a useful high temperature material.
When the sintered body is prepared under the same conditions for molding and sintering, characteristics of the resultant sintered body is greatly affected by the particle size, the particle size distribution and the shape of particles of aluminum nitride powder to be used as starting material powder.
In general, the aluminum nitride powder is prepared by a method in which aluminum powder is directly nitrogenated or a method in which aluminum powder is reduced with carbon and then nitrogenated. In these methods, however, it is very difficult to prepare aluminum nitride powder having small particle size and small particle size distribution and also having a uniform shape of particles. Moreover, in the latter method, the synthesis reaction must be carried out at high temperature and over a long period of time because of the chemical stability of alumina, thereby involving a problem that makes the method industrially disadvantageous.
In order to solve such a problem, in particular, the problem in the latter method, a method has been proposed in which a starting material powder comprising a mixture of aluminum hydroxide powder and a carbonic substance is incorporated with one or more of compounds selected from the group consisting of fluorides, iron, magnesium oxides, calcium oxides, oxides of iron, oxides of nickel, oxides of cobalt, oxides of chromium, oxides of manganese, oxides of vanadium and oxides of niobium, and the resultant mixture is heated at 1300 .degree. to 1600.degree. C. in a nitrogen atmosphere (see Japanese Patent Publication No. 51483/1984).
The above method surely makes it possible to carry out the synthesis reaction at a lower temperature. However, the resultant aluminum nitride powder can not be the one satisfying the small particle size, the small particle size distribution and the uniform shape of particles as aimed in this invention.